Add #![rustfmt::skip] to some compiler documentation code

These examples feature Rust code that's presented primarily to
illustrate how its compilation would be handled, and these examples are
formatted to highlight those aspects in ways that rustfmt wouldn't
preserve. Turn formatting off in those examples.

(Doc code isn't formatted yet, but this will make it easier to enable
doc code formatting in the future.)

Author: joshtriplett

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -418,6 +418,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// For example:
     /// ```
+    /// #![rustfmt::skip]
     /// fn foo<'a, 'b>( /* ... */ ) where 'a: 'b { /* ... */ }
     /// ```
     /// would initialize two variables like so:

compiler/rustc_hir/src/def.rs

@@ -357,6 +357,7 @@ impl DefKind {
 /// an associated `Res`:
 ///
 /// ```
+/// #![rustfmt::skip]
 /// fn str_to_string(s: & /* Res */ str) -> /* Res */ String {
 ///     /* Res */ String::from(/* Res */ s)
 /// }

compiler/rustc_mir_dataflow/src/impls/initialized.rs

@@ -107,6 +107,7 @@ impl<'tcx> MaybePlacesSwitchIntData<'tcx> {
 /// dataflow information shown in the right-hand comments.
 ///
 /// ```rust
+/// #![rustfmt::skip]
 /// struct S;
 /// fn foo(pred: bool) {                        // maybe-init:
 ///                                             // {}
@@ -196,6 +197,7 @@ impl<'a, 'tcx> HasMoveData<'tcx> for MaybeInitializedPlaces<'a, 'tcx> {
 /// dataflow information shown in the right-hand comments.
 ///
 /// ```rust
+/// #![rustfmt::skip]
 /// struct S;
 /// fn foo(pred: bool) {                        // maybe-uninit:
 ///                                             // {a, b, c, d}
@@ -288,6 +290,7 @@ impl<'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
 /// dataflow information shown in the right-hand comments.
 ///
 /// ```rust
+/// #![rustfmt::skip]
 /// struct S;
 /// fn foo(pred: bool) {                        // ever-init:
 ///                                             // {          }